Even after the use of so-called conventional methods of oil recovery, such as water injection and the immiscible injection of gas, a large part by volume of the original amount of oil in an oil deposit remains in the reservoir rock, having not been recovered.
In the case of reservoirs containing oils having a high viscosity, the use of these conventional methods of recovery does not provide satisfactory results. The high viscosity of the oil is an obstacle to its movement within the porous medium, while the injected fluid, water, or gas has a much greater mobility. This results in low coverage efficiencies and, as a result, normally very low or practically non-existent additional recovery. Similarly, high interfacial tension between the water and the oil lead to the retention of high quantities of oil in the region invaded by the water. The injected fluid thus does not succeed in withdrawing the oil from the pores of the reservoir, and gives low transport efficiencies as a result.
These are the two principal aspects that interfere in the processes of transport of fluid by fluid, and consequently are the points of operation of the special methods for recovery, which are also referred to as advanced recovery methods. These advanced recovery methods can be separated into thermal, chemical, and biological methods. Among the chemical methods used to improve the recovery factor of reservoirs with a high water flow, the injection of microemulsions stands out as the technology with the highest recovery potential.
The state of the art has various examples of how these recovery methods function, such as U.S. Pat. No. 3,983,940, which describes a composition and a method of injection of a microemulsion in a reservoir for the recovery of oil. The proposed microemulsion contains oil, refined or crude, an aqueous phase (brine at concentration of 2.5%), and an orthoxylene sulfonate as surfactant.
Another example can be found in U.S. Pat. No. 4,008,769, which describes a method for advanced recovery of oil from a subterranean formation by the injection of a microemulsion made up of an aqueous phase containing neutralized organic acids extracted from the oil, as well as an oil and a co-surfactant.
U.S. Pat. No. 4,240,504 describes a method of advanced recovery of oil where two immiscible phases (one microemulsion and one aqueous) are injected simultaneously into the subterranean formation.
The state of the art in relation to the methods of advanced recovery of oil employing microemulsions is vast. However there is also a need for a technical solution for a composition of microemulsion that is economically viable for the recovery of heavy oils.